3:30 PM - 4:30 PM
[J06-P-14] Network-MT survey in the vicinity of area with a forthcoming slow slip event in the SW part of Shikoku Island, SW Japan
○Makoto Uyeshima1, Maki Hata1, Hiroshi Ichihara2, Ryokei Yoshimura3, Koki Aizawa4 (1.Earthquake Research Institute, the University of Tokyo, Tokyo, Japan, 2.Graduate School of Maritime Sciences, Kobe University, Hyogo, Japan, 3.Disaster Prevention Research Institute, Kyoto University, Kyoto, Japan, 4.Institute of Seismology and Volcanology, Kyushu University, Fukuoka, Japan)
In the Bungo channel region at the western margin of the Nankai megathrust rupture zones, the long-term slow slip events (SSE) repeatedly occurred about every 6 or 7 years and we expect the next event soon. The SSE also activate deeper episodic tremors and slips (ETS) on the plate interface.
In order to examine influence of interstitial fluids on occurrence of the SSE and/or ETS activities, we have started the Network-MT survey in the western part of the Shikoku Island facing the Bungo channel since April, 2016. We use metallic telephone line network of the Nippon Telegraph and Telephone Corp. to measure the electrical potential difference with long baselines of from several kilometers to 10 and several kilometers. We selected 17 areas in the western part of Ehime and Kochi prefectures and installed 3 or 4 electrodes in the respective areas. The electrical potential differences measured in this way are known to be less affected by small scale near-surface lateral resistivity heterogeneities. We also measure geomagnetic field at two stations in the target region. With the aid of the BIRRP code, we could estimate the frequency-domain response functions between each voltage difference and the horizontal magnetic fields from 5 s to 10^5 s. We will show spatial characteristics of the responses and their preliminary 3-D interpretation to estimate regional electrical resistivity structure with the aid of a DASOCC 3-D inversion code.
This study is supported by JSPS KAKENHI Grand Number JP16H06475 in Scientific Research on Innovative Areas “Science of Slow Earthquakes. It is also partly supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan, under its Earthquake and Volcano Hazards Observation and Research Program. We acknowledge staffs of the Nippon Telegraph and Telephone WEST Corporation for their cordial support in the survey. We also thank Drs. H. Abe, A. Takeuchi and Y. Suwa for their help in preparing and installing instruments.
In order to examine influence of interstitial fluids on occurrence of the SSE and/or ETS activities, we have started the Network-MT survey in the western part of the Shikoku Island facing the Bungo channel since April, 2016. We use metallic telephone line network of the Nippon Telegraph and Telephone Corp. to measure the electrical potential difference with long baselines of from several kilometers to 10 and several kilometers. We selected 17 areas in the western part of Ehime and Kochi prefectures and installed 3 or 4 electrodes in the respective areas. The electrical potential differences measured in this way are known to be less affected by small scale near-surface lateral resistivity heterogeneities. We also measure geomagnetic field at two stations in the target region. With the aid of the BIRRP code, we could estimate the frequency-domain response functions between each voltage difference and the horizontal magnetic fields from 5 s to 10^5 s. We will show spatial characteristics of the responses and their preliminary 3-D interpretation to estimate regional electrical resistivity structure with the aid of a DASOCC 3-D inversion code.
This study is supported by JSPS KAKENHI Grand Number JP16H06475 in Scientific Research on Innovative Areas “Science of Slow Earthquakes. It is also partly supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan, under its Earthquake and Volcano Hazards Observation and Research Program. We acknowledge staffs of the Nippon Telegraph and Telephone WEST Corporation for their cordial support in the survey. We also thank Drs. H. Abe, A. Takeuchi and Y. Suwa for their help in preparing and installing instruments.